The present invention relates to apparatus for wrapping products with plastic film.
Prior art apparatus used for this purpose comes in numerous different kinds and designs and, in a first solution for palletised products, which will be described here purely by way of example, may consist of a supporting frame, usually in the form of a gantry structure, and a roll mounting carriage supported by a structure which is in turn supported by the supporting frame. The supporting frame is normally located near a roller or belt conveyor or a similar transporting system which feeds the products to be wrapped. The incoming products are usually already positioned on a pallet suitable for subsequent handling and transportation.
The roll mounting carriage supports a roll of plastic stretch film and, usually, a unit for unwinding and pre-stretching the film wound on the roll. The pre-stretching unit consists of one or more rotating power rollers driven by an electric motor (through suitable transmission means) mounted on the carriage itself. The film is unwound from the roll and wound onto the power rollers of the pre-stretching unit before being placed over the products to be wrapped.
The supporting structures are of two basic types: one with an arm in the shape of an upturned L and the other orbital, shaped like a ring. The supporting structure, of whichever type, is designed to move the carriage along a closed path (either circular or helical) about a vertical axis substantially coinciding with the vertical axis of the products to be wrapped, positioned on the pallet. Thus, the roll is made to rotate around the products and, depending on requirements and the size of the products concerned, may also be made to rise and fall along the vertical axis of the products so as to completely wrap the products from top to bottom with two or more windings of film. Usually, during the wrapping process, the film is stretched, that is to say, xe2x80x9cpulledxe2x80x9d lengthways, by the pre-stretching unit. The purpose of stretching the film before placing it on the products is twofold: to save on the amount of film used and to suitably tension it so as to improve its adhesion to the products, especially if the products are in tall stacks.
The present disclosure relates in particular to an orbital type supporting structure. In a supporting structure of this type, a ring mounted on the supporting frame is raised off the floor and moved up and down along the frame. At the same time, the roll mounting carriage, which is supported by the ring, is guided around the products by the ring. The ring is raised and moved up and down by drive motors, while the roil mounting carriage is driven along the wrapping path around the ring by an electric motor mounted on the roll mounting carriage itself.
Both the electric motor that drives and rotates the carriage and the electric motor that drives the pre-stretching unit are powered through sliding contact connections positioned and operating on the supporting guide ring.
The supporting ring structure, however, has several disadvantages which limit its field of application and which are due, in particular, to the sliding contact connections. Connections of this type prevent the construction of high efficiency protections, which means that the apparatus can only be installed in environments with a high humidity.
Further, sliding contacts are subject to heavy wear and do not permit high operating speeds to be reached, and this significantly limits the productivity of the apparatus.
To overcome these disadvantages, the Applicant devised an apparatus, disclosed in European patent EP-811.554, including a structure to support the roll mounting carriage and a pre-stretching unit driven by a respective electric motor. The supporting structure comprises a raised mobile structure mounted on the supporting frame and a rotatable ring mounted on the raised mobile structure and rotated about its axis by a motor anchored and kinematically connected to the raised mobile structure. The carriage is attached to the rotatable ring and mounts an electric generator designed to power the electric motor of the pre-stretching unit whose shaft is maintained in permanent kinematic connection with an annular toothed track attached to the raised mobile structure.
This solution solved many of the problems caused by the power supply of the previous solution, although the presence of a second ring and the higher number of power supplies and electrical connections had the effect of increasing the cost of constructing the apparatus.
The description and drawbacks outlined above also apply, but with some of the technical details differing, to apparatus where the ring structure extends in a vertical plane and the products move in a horizontal direction through the ring and are wrapped in successive windings of film along a horizontal wrapping axis.
The present invention has for an object to provide, as a valid alternative to the structural solution described above, a product wrapping apparatus whose wrapping structure has been greatly simplified, with highly reliable sturdy components, while maintaining the same high speed and wrapping quality features.
Another object of the invention is to provide a wrapping apparatus that can be easily adapted to wrap products either along a vertical axis or along a horizontal axis.
Accordingly, the present invention provides an apparatus for wrapping products with plastic film and comprising: a ring-shaped element supporting a carriage that moves around the ring-shaped element; drive means for moving the ring-shaped element relative to the group of products to be wrapped; main motor means associated to the ring-shaped element and designed to drive the carriage. The carriage mounts a roll of plastic film and a pre-stretching unit driven by suitable drive means. The pre-stretching unit comprises a pair of rollers for pre-stretching the film and a transmission and control roller that swings towards and away from the group of products, and is designed to start or stop film feed according to its position relative to the products to be wrapped. The drive means comprise a kinematic chain consisting of the main motor means and a ring-shaped, continuous drive take-off track for the pre-stretching unit drive means which comprise an engage/release unit connected to and controlled by the transmission roller and designed to transmit drive from the ring-shaped track to the pair of pre-stretching rollers according to the position of the transmission roller.